Pneumatic tire wear indicating tread pattern

ABSTRACT

A pneumatic tire and moulding matrix therefore, the tire tread incorporating a traction pattern which changes distinctively when only a predetermined amount of tread rubber remains, thus warning the tire user that his tire is approaching the legal or safe limit and will soon have to be replaced or retreaded.

This invention relates to pneumatic tires.

According to the invention a pneumatic tire comprises a tread providedwith at least one main drainage groove and a first, radially outer, anda second, radially inner, pattern each comprising one or moreradially-disposed slots, sipes, grooves, incisions, holes or the like,the first pattern changing to the second pattern at a level situatedradially inwardly of and substantially parallel to the treadground-contacting surface of the tire, said level being a predeterminedamount less than the depth of the main drainage groove, the secondpattern being distinctively different from the first and comprising awholly radial continuation of part only of said first pattern.

Preferably the second pattern is substantially undetectable from theexterior of the tire until at least a portion of the tread equal indepth to the first pattern has been worn away.

Preferably the said predetermined amount is somewhat greater e.g. 1 mm.greater, than the minimum tread pattern depth allowed under local lawsor regulations, e.g. 1 mm. or 2 mm., so that adequate prior warning isgiven to a tire user that the legal limit of wear is approaching.

The second pattern is preferably so distinctively different from thefirst pattern that the tire user's mind is directly associated with thefact that in due time the tire will become unsafe or illegal if it iscontinued to be used and that it should be changed. For example, thesecond pattern may be in the form of a warning word or several warningwords repeated around the tire circumference and/or across part at leastof the tire tread width.

The invention also includes a pneumatic tire as described in any of thepreceding paragraphs in which said second pattern changes to a thirdpattern, and perhaps to subsequent patterns, below the treadground-contacting surface.

All of the patterns previously referred to are preferably formed bymoulding, but any other suitable method e.g. cutting or drilling, may beused.

According to the invention also a tire moulding matrix comprises aplurality of projections on the tread moulding surface of the matrix theprojections being for moulding a first, radially outer, and a second,radially inner, pattern in the tread of the tire incorporating at leastone main drainage groove, the configuration of at least part of at leastone of the said projections changing distinctively at a predeterminedlevel which is substantially parallel to the surface of the matrix formoulding the tread ground-contacting surface of the tire and which issituated at a depth which is a predetermined amount less than the depthof the projection for moulding the main drainage groove, the said secondpattern comprising a wholly radial extension of part only of said firstpattern.

Embodiments of the invention will now be described by way of examplewith reference to the accompanying drawings of which:

FIG. 1 shows a fragmentary perspective view of a tread moulding matrixaccording to a first embodiment of the invention.

FIG. 2 shows a fragmentary perspective view of a tread moulding matrixaccording to a second embodiment of the invention.

FIG. 3 shows a plan view of part of the first pattern of the tread of atire according to the second embodiment.

FIG. 4 shows a plan view of part of the second pattern of the tread of atire according to the second embodiment.

A first embodiment comprises a pneumatic car tire the tread pattern ofwhich is moulded by a conventional method using a mould comprising amatrix 1 (part of which is shown in FIG. 1) which is provided with aplurality of ribs 2 and pins 3 and 4. The ribs, 8 mm. high and ofzig-zag configuration extend generally circumferentially of the mouldand form generally circumferential grooves, each 8 mm. deep, in the tiretread. The pins, some (indicated by the reference numeral 3) of whichare 6 mm. high and the remainder (indicated by the reference numeral 4)8 mm. high, form a pattern of holes in the tire tread ribs between thegrooves.

The construction of the mould matrix is such that the pins and ribsthereof can be readily withdrawn in a radial direction from the tread ofthe moulded tire. When 6 mm. i.e. the first pattern, of tread has beenworn away in use of the tire that part of the tread pattern formed bythe 6 mm. holes disappears leaving only that portion formed by the 8 mm.deep holes, i.e. the second pattern and the grooves. The 8 mm. deepholes form the word STOP repeated round the tire circumference which isnot readily apparent in the unworn state of the tire, (being camouflagedby the 6 mm. deep holes) and which warns the motorist that there is only2 mm. of tread rubber remaining in that area of the tread surface i.e.his tire will soon become unsafe and probably illegal and that he shouldreplace the tire before further wear may render it unsafe to use. Wordsother than STOP could be used either additionally or alternatively.

In a modified form (not illustrated) of the first embodiment some or allof the pins are enlarged at their extremities so that a bulbous chamberis formed at the base of some or all of the holes formed in the tiretread. Preferably only the 8 mm. pins are enlarged 2 mm. from their endsso that a chamber 2 mm. deep is formed in the tire. Thus when 6 mm. oftread has been worn away a more distinctive pattern appears to warn themotorist. In addition the drainage of a tire tread provided with bulbouschambers is better compared with that of a tire not so provided,especially at the time of the tire's life when only 2 mm. of treadremains.

A second embodiment (as shown in FIGS. 2, 3 and 4) of the inventioncomprises a tire (see FIG. 3) having a tread provided with a pluralityof grooves 5 and slots 6 some of the slots or part of each slot openingout into a substantially cylindrical chamber situated radially inwardlyof the tread surface with its axis parallel thereto. This tire ismoulded by means of a moulding matrix 7 (see FIG. 2) provided with ribs2 (to form grooves) and knife blades 8 (to form the slots) some of whichor part of each of which have joined thereto, e.g. by welding, or haveintegrally formed therewith a cylindrical portion 9 e.g. a wire or rod,of diameter greater than the thickness of the knife blades. Thecylindrical portion 9 wire or rod is bent into the form of a letter in aplane parallel to that surface 10 of the matrix for moulding theground-contacting surface of the tread, while the knife blade to whichit is joined has a similar form with one or more additional features(for example that part of a blade shown as 11 in FIG. 2) so aseffectively to disguise the identity of the letter. Several of theseblades with the wire letters attached are incorporated in the tiremoulding matrix, the several letters forming the mirror image of thewarning word STOP. The knife blades thus form the first pattern in thetread while the wires or rods form the second pattern.

In use of a tire moulded in this way when most of the tread has beenworn away the chambers appear (as shown in FIG. 4) and because they arewider than the slots and in the form of a warning word should besufficiently distinctive to cause the motorist to be conscious of theneed soon to renew the tire.

In a first modification (not shown) of this second embodiment, the tiretread is provided with a pattern of slots some of which or part of eachof which do not open out into chambers but merely are constructed to bedeeper than the remainder of each slot or slots. This pattern is mouldedusing a matrix incorporating knife blades some of which or part of eachof which are deeper than the remainder of each blade or the blades. Thedifference between the two depths of blade or blades can be 2 or 3 mm.i.e. equal to the local minimum allowable tread depth plus an amount toprovide a warning of the need to replace the tire without undue delay.

In a second modification (not shown) of the second embodiment the slotsand chambers are moulded by means of a matrix provided with knife bladesand to which are weakly attached e.g. by means of a weak adhesive orthin textile fibers the aforementioned wire letters. In addition theseletters are all wired to each other to form a ring which extends aroundthe internal circumference of the tire mould on the radially innerextremities of the blades.

After moulding and on removal of the moulding matrix from the tire thering of letters remains embedded in the tire tread, the textile fibersor the adhesive bond having broken during said removal. The ring ofletters is removed in a separate operation.

It is an advantage of this modification that the second pattern i.e. theletters may be changed without changing the complete mould matrix.

In a third modification (not shown) of the second embodiment the wiresor rods are replaced by U or V channels in which a thin strip ofmaterial may be retained during moulding but leaves the channel onremoval of the tire from the mould. Thus the moulding operationeffectively embeds this strip into the tread rubber at the base of theslot or slots.

The material inserted into the chambers should be such as to make theappearance of the second pattern, when the tread has worn awaysufficiently to expose it, even more distinctive. For example,vulcanized or unvulcanized rubber or plastics material may be insertedof a color different from the remainder of the tread rubber. Thus, forexample, when sufficient tread has worn away a colored word appears inthe tread to warn the motorist of the small amount of tread rubberremaining. Other examples of materials which may be inserted arematerials which generate a noise on becoming uncovered when the tread issufficiently worn, textile cords, or rubber of greater or lesserabrasion resistance than the tread rubber. In this last example thewords of rubber will stand proud of or recessed below, respectively, thetread surface. It can be arranged either that the inserted materialremains to form part of the wearing surface of the tread or becomesdetached under the influence of centrifugal force to leave remaining arecognisable impression in the tread rubber.

Having now described my invention what I claim is: .[.1. A pneumatictire comprising a tread provided with at least one main drainage grooveand a first, radially outer, and a second, radially inner, pattern eachcomprising at least one tread element selected from the group consistingof slots, sipes, grooves, incisions and the like, the first patternchanging to the second pattern at a level situated radially inwardly ofand substantially parallel to the tread ground contacting surface of thetire, said level being a predetermined amount less than the depth of themain drainage groove, the second pattern being distinctively differentfrom the first and being located immediately radially inwardly of and inradial alignment with said first pattern..]. .[.2. A pneumatic tireaccording to claim 1 wherein the second pattern is substantiallyundetectable from the exterior of the tire until at least a portion ofthe tread equal in depth to the first pattern has been worn away..]..[.3. A pneumatic tire according to claim 1 wherein the second patternis in the form of at least one warning word..]. .[.4. A pneumatic tireaccording to claim 1 wherein the second pattern is in the form of atleast one warning word repeated around the tire circumference..]. .[.5.A pneumatic tire according to claim 1 wherein the second pattern is inthe form of at least one warning word repeated across the tire treadwidth..]. .[.6. A pneumatic tire according to claim 1 wherein the secondpattern comprises a plurality of chambers..]. .[.7. A pneumatic tireaccording to claim 1 wherein the second pattern is at least partiallyfilled with a material distinctively different from the tread rubber..]..[.8. A pneumatic tire according to claim 7 wherein the said materialcomprises a rubber or plastics material of a color different from thetread rubber..]. .[.9. A pneumatic tire according to claim 7 whereinsaid material has an abrasion resistance different from that of thetread rubber..]. .[.10. A pneumatic tire according to claim 1 whereinthe second pattern changes to at least one subsequent patternradially-inwardly thereof..]. .[.11. A pneumatic tire copmrising a treadprovided with at least one main drainage groove and a first, radiallyouter pattern of no particular visual significance and a second,radially inner, pattern having visual significance, each patterncomprising at least one tread element selected from the group conistingof slots, sipes, grooves, incisions and the like, the first patternchanging to the secnd pattern at a level situated radially inwardly ofand substantially parallel to the tread ground-contacting surface of thetire, said level being a predetermined amount less than the depth of themain drainage groove, the second pattern having a lesser number of treadelements than the first pattern with all of the second pattern treadelements being in radial alignment with corresponding elements of thefirst pattern and located immediately radially inwardly of similar treadelements in the first pattern so that when the first pattern is wornaway the second visually significant pattern is exposed..].
 12. Apneumatic tire comprising a tread provided with at least one maindrainage groove and a first, radially outer, and a second, radiallyinner, pattern each comprising at least one tread element selected fromthe group consisting of slots, sipes, grooves, incisions and the like,the first pattern changing to the second pattern at a level situatedradially inwardly of and substantially parallel to the tread groundcontacting surface of the tire, said level being a predetermined amountless than the depth of the main drainage groove, the second patternbeing distinctively different from the first, being located immediatelyradially inwardly of and in radial alignment with said first pattern,and being in the form of at least one warning word.
 13. A pneumatic tirecomprising a tread provided with at least one main drainage groove and afirst, radially outer, and a second, radially inner, pattern eachcomprising at least one tread element selected from the group consistingof slots, sipes, grooves, incisions and the like, the first patternchanging to the second pattern at a level situated radially inwardly ofand substantially parallel to the tread ground contacting surface of thetire, said level being a predetermined amount less than the depth of themain drainage groove, the second pattern being distinctively differentfrom the first, being located immediately radially inwardly of and inradial alignment with said first pattern, and being in the form of atleast one warning word repeated around the tire circumference.
 14. Apneumatic tire comprising a tread provided with at least one maindrainage groove and a first, radially outer, and a second, radiallyinner, pattern each comprising at least one tread element selected fromthe group consisting of slots, sipes, grooves, incisions and the like,the first pattern changing to the second pattern at a level situatedradially inwardly of and substantially parallel to the tread groundcontacting surface of the tire, said level being a predetermined amountless than the depth of the main drainage groove, the second patternbeing distinctively different from the first, being located immediatelyradially inwardly of and in radial alignment with said first pattern,and being in the form of at least one warning word repeated across thetire tread width.